Increasing air pollution is a serious concern, and therefore the purification of gas emissions is becoming more and more important every year. The largest source of emissions of harmful gases into the atmosphere are energy enterprises and automobile transport.
Purification of gas emissions is carried out in various ways, among which the catalytic method of neutralizing and lowering the concentration of pollutants to the maximum permissible level is the most effective in many cases. Catalytic purification is also preferred for economic reasons.
As a rule, catalytic methods are universal and can be used for deep purification of various process gases. Using this method, industrial gases can be cleaned of oxides of nitrogen and sulfur, carbon monoxide, harmful organic compounds and other toxic impurities. In this case, harmful impurities are converted into less harmful and harmless, and sometimes even useful ones. In the same way the exhaust gas is cleaned. In fact, this method consists in implementing the processes of chemical interaction of substances in the presence of catalysts, which leads to the conversion of impurities to be neutralized into other products.
Special catalysts accelerate chemical reactions, but do not affect the energy level of interacting molecules and do not shift the equilibrium of simple reactions. Catalytic purification is promising for multicomponent mixtures of exhaust gas streams. For the purification of gases in industry, oxides of iron, copper, chromium, cobalt, zinc, platinum and others are used as catalysts. These substances are used to process the catalyst carrier placed inside the reactor apparatus. It is necessary to monitor the integrity of the outer catalyst layer, otherwise the catalytic purification will not be carried out in full, and the emission of harmful substances may exceed permissible limits.
The main requirement for the catalyst is the stability of the structure during the reaction. The search and manufacture of catalysts, not only suitable for long-term use, but also quite cheap, is a certain difficulty that limits the application of the catalytic method. Modern catalysts must have selectivity and activity, resistance to temperature and mechanical strength.
Industrial catalysts are made in the form of blocks and rings of a honeycomb structure. They have a low hydrodynamic resistance and a high external specific surface. Most often, catalytic purification of gases in a fixed catalyst is used.
In industry, it is possible to use two fundamentally different methods of gas purification processes — a stationary and an artificially created non-stationary mode. The transition to the predominant use of the non-stationary method is due to a higher technological process, an increase in the reaction rate, an increase in selectivity, a decrease in the energy intensity of the processes, a decrease in the capital costs of the installation and a decrease in the costs of its operation.
The main direction of the development of catalytic methods is to create cheap catalysts that can operate at low temperatures and be resistant to various substances. For a concentration below 1 g / m³ and with large volumes of purified gases, the thermocatalytic method requires high energy consumption and a huge amount of catalyst, so there is a need to develop the most energy-saving processes and equipment that require low capital costs.
